I call this having "Complimentary" skill sets. If an OO shop, Java vs .NET and Ruby/Python etc. Hire for smart, ambitious, willing candidates that fit in well with the culture. I've seen people switch tech stacks very quickly, especially when there's established patterns in the existing code base they can pick up on.

I think programming language/tech stack is about 8th on my list of deciding on where to work, etc. (This just inspired me to do some writing on the subject, since I've delivered systems in most major tech stacks over the years.)